Aircrafts typically include a plurality of flight control surfaces that, when controllably positioned, guide movement of the aircraft through the air. The number and type of flight control surfaces included in an aircraft may vary, but typically both primary flight control surfaces and secondary flight control surfaces are included. The primary flight control surfaces are those that are used to control aircraft movement about the pitch, yaw and roll axes, and the secondary flight control surfaces are those that are used to influence the lift or drag (or both) of the aircraft. Although some aircraft may include additional control surfaces, the primary flight control surfaces typically include a pair of elevators, a pair of ailerons and a rudder, and the secondary flight control surfaces typically include a horizontal stabilizer, and a plurality of flaps, slats and spoilers.
Modern aircrafts have horizontal stabilizers located at the tail section of the fuselage or the rudder section that are pivotably supported relative to the airplane fuselage to “trim” the aircraft during flight by selective adjustment by the pilot via an internal control unit. Adjusting the position of the horizontal stabilizer by a stabilizer actuator accommodates different load distributions within the aircraft and different atmospheric conditions, i.e. wind, rain, snow, temperature variation, etc. The stabilizer is traditionally pivotably connected to the tail section of the fuselage at a point along its length, such as generally midway along its length.
Conventional trimmable horizontal stabilizer actuators consist of a ballnut assembly connected with an actuating drive gimbal which is pivotably connected to one end of the horizontal stabilizer structure. The ballnut assembly includes a ballnut housing and a ballscrew extending axially and usually vertically through the ballnut housing and through a drive gimbal housing. The ballnut housing is connected to the drive gimbal housing by a trunnion segment. The ballscrew, in turn, may have its proximal end remote from the actuating drive gimbal and may be fixed from translation or axial movement by a connection to a second, support gimbal which is typically pivotably secured to the tail section.
As the ballscrew is rotated, the drive gimbal and ballnut housing will be moved in translation. Thus, as the ballscrew is rotated in one direction, the ballnut housing is moved towards the ballscrew distal end and the leading edge of the horizontal stabilizer is pivoted upward in a first direction. On the other hand, by rotating the ballscrew in an opposite direction, the ballnut housing is moved toward the ballscrew proximal end and the leading edge of the horizontal stabilizer is pivoted downward in a second direction. Rotation of the ballscrew is routinely effected by a motor and associated gearing which is actuated by the pilot via the internal control unit.
The aforementioned linear output actuator may be generally suitable for actuating different flight control surfaces. However, the linear output actuator may not be suitable for directly supporting a hinged flight control surface, such as an aileron located at a trailing edge of an aircraft wing. Actuating the hinged flight control surface may include coupling the linear output actuator to the hinged flight control surface via a horn arm lever for transforming the linear motion into rotary motion. Using the horn arm lever may be disadvantageous in that the articulation of the lever and the associated components used to perform the linear to rotary transformation may require more envelope than the wing height, particularly in aircraft designs where the wings are thin.
Rotary geared actuators and rotary vane hydraulic actuators have been used for controlling hinged flight control surfaces. However, rotary vane hydraulic actuators have inherent sealing and packaging issues. Rotary geared actuators have inherent complexity in motor drives, higher jamming failure rates, damping issues and back-driving limitations, in that rotary geared actuators are generally not capable of back-driving when the actuator is unpowered or in a failure state. Helical actuators may also be deficient in that helical actuators may also be incapable of back-driving.